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rossiz

Out with the new, in with the old...

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managed to have a productive long weekend in spite of the temptations (beer & brats, etc.) 

turned back the z technology clock a little: ripped out the efi and associated spaghetti/plumbing and installed the su's.

 

the worst part of the whole process was installing the choke lever... i picked up one of those tunnel-mount plates in order to avoid breaking the underside of the console (the choke lever set came with the telltale chunk of broken plastic mounting post still attached to the mounting screw) and it was a bit of a pain to set the layout on the tunnel so the choke lever would line up in the console slot. every time i have to do work on the interior (especially under the dash) i wish to god i had a chevy van instead... contortions upside down, holding a flashlight in my teeth, having my glasses fog and dropping the fastener on my forehead for the 5th time... but eventually it worked out just fine. i had purchased a 240z choke cable fire wall grommet but it turns out i didn't need it. what i had assumed was a metal blank-off plate next to the throttle linkage turned out to be a dual-opening rubber blank. so i just drilled two holes in it and the choke cables go through with a nice airtight seal.

 

getting the manifold off was cake thanks to the multiple head swaps i've done and i went ahead and pulled the afm, charcoal cannister and associated mounting brackets as well. i left the wire harness in for now, coiled up and tucked out of the way by the windshield washer bottle.

 

i'm using the stock fuel filter & lines for now, but will revise when some parts come in. 

 

next was swapping out the efi fuel pump with a cute little airtex unit. mounted it up near the moustache bar and looped the fuel line over to the existing hardline. i left all the efi wiring/relays/etc. in place, so it all works exactly as previous - just a lot less pressure. the airtex pump is so quiet, i had to put my hand on it to make sure it was working - nice.

 

i then got the carbs mounted up and checked the float levels. interesting side note: i had done this previously in my basement using water, with the fuel pump wired to a power supply and a juice glass as a see-thru bowl. even though i had both set dead-on to 23mm they were quite off when i put them on the car. not sure if it has to do with the density difference between gas and water, the tilt on the car or what, but i eventually got them both to 23mm (again). i used some clear vinyl tubing as a temporary sight glass which was quite helpful these first times around.

 

she fired up quickly and after warm-up i synched them at idle and high-speed w/the old unisync that i've had for decades in my tool box. worked a treat.

 

took her out for a test drive and was sorely disappointed... no power, burbled and popped horribly on decel, wouldn't rev, no fun. it sounded like the mixtures were way out of sync, and i couldn't get them to match up. decided to do another float level adjust, but this time i figured i'd go for the fuel in the jet nozzle rather than the height of the float bowl. read on one of the blogs out there that the recommended fuel level corresponds exactly to 1cm (10mm) below the bridge, which you can check by turning down the jet adjusters 10 full turns (1mm each) and fuel should be right at the top of the jet nozzle. turns out that i needed the rear bowl to be set about 5mm higher (18mm down, vs. the 23) in order for the nozzle to get its fuel at 1cm down. not sure why... 

 

she ran much better and is now quite driveable, although still not perfect - i ran out of daylight so will need to do more testing/tuning. next step will be setting up the dual-sensor afm so i can get a better idea of what's going on vs. just reading plugs. 

 

stay tuned...

 

carbs on - ready to run

post-28907-0-86692200-1432620246_thumb.j

 

 

temp sight glass setup

post-28907-0-44098300-1432620249_thumb.j

 

 

 

 

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You live my Walter Mitty dreams. I have dual downdraft Webers installed by a previous owner and while it drives fine, I yen to return the car back to the original SUs. Strangely, I have no similar desire to re-install the air pump.

 

BTW during my recent overhaul, I pulled the engine without transmission from the passenger side. Before removing I checked the angular orientation to facilitate re-installation. I found the block tilted some 3 degrees and this is why you float level changed when you installed them.

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A couple of tuning tricks:

 

Fuel Level:

The fuel level should be 20mm down from the bottom of the gasket that seals the roof. ZKars found this detail out as the 23mm is actually from the inside roof.

 

0 Turn Calibration:

When setting the needle in the piston, remove the piston, turn the jets all the way up until they stop. You should see them flush or slightly above the bridge. Next pull the needle out so that the shoulder is ~ 3mm below the bottom of the piston and adjust the needle holding screw so that you can barely push the needle in by hand. Now with the needle out 3mm, place the piston back and force it down so the that the shoulder on the needle mates firm against the top of the jet when the piston is pushed all they way down. Now tighten the needle in this location.  This procedure accurately sets "0 turns" for each carb with the nozzle and the jet at 0 gap.

 

Idle Fuel and Balance:

When setting the idle, disconnect linkage to carbs (pop a ball and socket on the vertical rod between the carbs) use unisyn to balance air flow with engine hot and jets at 2.5 turns down. Next disable the back carb by sticking your finger in and lifting the piston. the car should stumble along just running on the front 3 cylinders. If not lower the front jet 1/2 a turn to give the front carb more fuel and try again. Do this until you can stumble along on the front carb while disabling the back.

 

Now repeat by disabling the front carb with your finger and try to get the jet height right for the back so that the car stumbles along on just the back 3 cylinders.

 

Now rebalance the air with the unisyn and do fine adjustments repeating the finger disabling.

 

Congrats you just balanced the carbs at idle which means nothing as you do not drive at idle :)  ... but it is a start.

 

 

 

Off-Idle Fuel and Balance:

 

Reconnect the push rod so that the linkage is now in place.

Turn the fast idle screw on the top of the linkage near the centre so that the carbs are at 3000rpm. (It will sound very exciting.)

Read the air flow to the front carb then match this to the back carb by adjusting the balance adjuster screw near the back carb (the screw is on the linkage between the carbs).

 

Next note the RPMS then disable the rear carb and note the rpms of just running on the front.

Repeat this but disable the front and note the rpms on the rear. Adjust the fuel jets so that the rpm drop is the same for both front and rear carb.

 

 Congrats, you just adjusted your car for  driving.

 

Tweaks

 

Since you may have adjusted for a nice balance BUT you may be a bit rich or lean, drive the car and read the plugs. turn both jets up or down the same amount until the colour and performance looks good. Repeat the off-idle balance test.

 

 

USING Wide band (reading all 6 cylinders together)

When setting the jet height at idle and doing the disable trick, aim for ~ 14.5 at idle on both carbs and ~29 when running on just the front three and ~ 29 when running on the back three

 

When setting the jet height off-idle and doing the disable trick, aim for  <14  at 3000rpm on both carbs and ~26 when running on just the front three and ~ 26 when running on the back three. I can't recall the exact numbers but the point is that the reading for the front 3 and the back 3 should be the same to balance the fuel.

Follow up with road tests to ensure a/f is normal for idle, cruise and driving under load.

 

No worries if you have problems with your 2nd hand carbs, I can bring a set of carbs out or parts when I visit in June. Just let me know.

Edited by Blue

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great info blue - couple questions (in red) below:

 

A couple of tuning tricks:
 
Fuel Level:
The fuel level should be 20mm down from the bottom of the gasket that seals the roof. ZKars found this detail out as the 23mm is actually from the inside roof.

 

yes - did this (actually used my digi capipers to measure roof height) and still found that the better measurement was the 1cm to jet nozzle test
 
0 Turn Calibration:
When setting the needle in the piston, remove the piston, turn the jets all the way up until they stop. You should see them flush or slightly above the bridge. Next pull the needle out so that the shoulder is ~ 3mm below the bottom of the piston and adjust the needle holding screw so that you can barely push the needle in by hand. Now with the needle out 3mm, place the piston back and force it down so the that the shoulder on the needle mates firm against the top of the jet when the piston is pushed all they way down. Now tighten the needle in this location.  This procedure accurately sets "0 turns" for each carb with the nozzle and the jet at 0 gap.

 

yes - did this (saw on the 'just su' video)
 
Idle Fuel and Balance:
When setting the idle, disconnect linkage to carbs (pop a ball and socket on the vertical rod between the carbs) use unisyn to balance air flow with engine hot and jets at 2.5 turns down. Next disable the back carb by sticking your finger in and lifting the piston. the car should stumble along just running on the front 3 cylinders. If not lower the front jet 1/2 a turn to give the front carb more fuel and try again. Do this until you can stumble along on the front carb while disabling the back.
 
Now repeat by disabling the front carb with your finger and try to get the jet height right for the back so that the car stumbles along on just the back 3 cylinders.
 
Now rebalance the air with the unisyn and do fine adjustments repeating the finger disabling.
 
Congrats you just balanced the carbs at idle which means nothing as you do not drive at idle :)  ... but it is a start.
 

so, if i'm gonna re-do the jets for off-idle, why don't i just do it for off-idle? i get balancing the linkage for even flow (did that) but not sure about the mixture. if i understand correctly, the flow balance is entirely about adjusting mechanical obstruction to the airflow (butterflies) and the mixture will only affect idle speed...
 
 
Off-Idle Fuel and Balance:
 
Reconnect the push rod so that the linkage is now in place.
Turn the fast idle screw on the top of the linkage near the centre so that the carbs are at 3000rpm. (It will sound very exciting.)
Read the air flow to the front carb then match this to the back carb by adjusting the balance adjuster screw near the back carb (the screw is on the linkage between the carbs).

 

yes - did this and got 'em nicely matched for flow

Next note the RPMS then disable the rear carb and note the rpms of just running on the front.
Repeat this but disable the front and note the rpms on the rear. Adjust the fuel jets so that the rpm drop is the same for both front and rear carb.

 

have not tried this yet - will do tonight when i get home from work (16 mile drive) and she's all warmed up 

Congrats, you just adjusted your car for  driving.
 
Tweaks
 
Since you may have adjusted for a nice balance BUT you may be a bit rich or lean, drive the car and read the plugs. turn both jets up or down the same amount until the colour and performance looks good. Repeat the off-idle balance test.
 
 
USING Wide band (reading all 6 cylinders together)
When setting the jet height at idle and doing the disable trick, aim for ~ 14.5 at idle on both carbs and ~29 when running on just the front three and ~ 29 when running on the back three
 
When setting the jet height off-idle and doing the disable trick, aim for  <14  at 3000rpm on both carbs and ~26 when running on just the front three and ~ 26 when running on the back three. I can't recall the exact numbers but the point is that the reading for the front 3 and the back 3 should be the same to balance the fuel.

Follow up with road tests to ensure a/f is normal for idle, cruise and driving under load.
 
No worries if you have problems with your 2nd hand carbs, I can bring a set of carbs out or parts when I visit in June. Just let me know.

 

yes - will do, and thanks for the offer! right now i think i might be ok but this week of driving will be a good test. 

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first real road report: drove her to work this morning (16 miles) and i'm pleased to say i'm extremely happy with the carbies!!

 

cold enrichment

about 50 degrees this morning, not exactly frosty but definitely cold enough for the efi system to have needed the csv and temp sensor enrichment circuit. half choke, no pedal and she started instantly - actually startled me. revved up to 2000 so i tapped the choke forward a little till the idle was at about 1500 and pulled out of the driveway. interestingly, the choke enrichment does a better job of cold-running than the efi systems ever did. used to be, it would start right up on the csv but run like a dog until the temp gauge started moving. wouldn't rev over 2500, stumbled and stuttered, sounded awful, but i was used to this and just limped the first few blocks until she warmed up. with the chokes engaged, she ran just fine from dead cold - revved fine, ran pretty much completely normal and as she warmed up i just tapped the lever down.

 

idle

rock-solid steady at 800 rpm and silky smooth. the efi would hunt a bit, kind of a 100 rpm drift which i could never pin down to a specific condition or fix.

 

performance

pretty close to where i was with the efi - i didn't get too crazy on my morning commute, so i'll need to rip around my local test roads to do a better butt-dyno comparison. in normal driving, it's identical to the efi - smooth, no stumbles, burps or farts. when i get the dual-lambda setup in place i'll be able to really check on the needles (using the sm set sent with my zt rebuild kit)

 

fuel economy

it just so happens that i had a full tank prior to the swap, so i should be able to check by the end of the week and report back.

 

have to say i'm impressed with these little buggers!

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so, if i'm gonna re-do the jets for off-idle, why don't i just do it for off-idle? i get balancing the linkage for even flow (did that) but not sure about the mixture. if i understand correctly, the flow balance is entirely about adjusting mechanical obstruction to the airflow (butterflies) and the mixture will only affect idle speed...

:) The idle adjustment is really just a practice run at the procedure as well as getting your idle speed set and fuel in the ball park.

The only things you can adjust on our carbs are:

1. Airflow at idle (butterfly stops)

2. Airflow balance at idle (butterfly stop difference between front and back)

3. Airflow balance off-idle (screw in connecting linkage)

4. Fuel flow at idle and off idle (jet height)

5. Fuel flow balance at idle and off idle (jet height difference between front and back)

6. Fuel flow transitions (damper oil)

7. Needle height vs rpm (spring pressure and weight of piston)

8. Fuel flow vs. needle height (needle taper)

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Congrats Rossiz, Looks like a painless transplant, if such exists. I have seen others having nightmares for weeks after, but you seem to have nailed it.

 

Chas

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thanks for all the kind words - i'm happy to have a simple mechanical system that i can understand and adjust, and it's a bonus that it appears to be working well so far.

 

the actual transplant was fairly painless (with the exception of spending several hours fiddling with the floats and the sore neck i have from installing the choke setup) but the work this weekend follows several weeks of work and research. i watched the 'just su' video a couple times, read a ton of su tuning/setup posts/blogs/etc. and got to know the hardware by doing a complete clean, polish & re-build. even after having thought through it dozens of times, i still had to run to the hardware store twice for various bits and pieces.

 

best tip i can give: glue the float bowl gaskets to the lids. they are a royal pita when they get wet and start to curl up. i used some permatex on mine and it held up long enough to do my adjustments (about 20 times) and towards the end they were starting to peel around the corners a bit.

 

blue - thanks for the list, it really sums it up. i've completed 1-4, will do 5 tonight, 6-8 are the points i've yet to tackle and will get into that when i have the O2 sensors hooked up so i'm not groping in the dark. for the damper oil, i just bought a $1.99 bottle of the carb oil from msa (looks like vegetable oil to me...) and just filled up the reservoirs. not very scientific, but a starting point.

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So it a case of the 7 P's

Prior and Propper Preperation Prevents wizz Poor Performance

Edit: Wtf "Wizz" is not what I wrote. Dam site census. Now it does sound right.

Edited by EuroDat

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thanks cap'n - i fabbed up a quick 'make-do' clamp to get me going but it will be great to have the proper bits on there! :)

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Hey Geoff

I'm doing the "Snoopy happy feet dance" for you in Portland. Your description of a cold start is spot on. Sounds like you're very close to perfect. You're gonna love the carbs. Who knows, Maybe you can even convince Sarah that they aren't evil. :)

Can't wait for the results from the butt-dyno run. So, is the new ignition sys. going to be installed, before or after the new build goes in?

Great job.

Mark

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thanks mark - the snoopy dance image is a hard one to let go of... i'll be chuckling all day about that one  :D

the distributorless ignition system is going on the new build - that will take some time to set up, so i'll do the initial install with the zx dizzy and then do the swap. i'm trying to do the engine in stages, setting up one system at a time and proving it out (carbs first on the current motor, then new motor w/existing dizzy, then the DIS) vs. doing it all at once and having to deal with the nightmare of having to troubleshoot/tune everything at once. the DIS also requires some programming, which will be easier once the engine is basically running and tuned.

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just a quick follow-up on this thread:

 

i completed my F54/P79 rebuild and swapped it in, transferring the carbs exactly as set up for the old motor and i've been delighted with how well it runs. the the new motor is broken in with about 700 miles on it and the carbs are performing flawlessly - beautiful, steady idle at 600rpm and silky smooth right up to 7K (haven't revved any further than that yet). i'm pretty sure there's more to get from them with some fine tuning, but that will wait until i install a 6-2-1 header and the dual O2 sensors to really understand where it's at. i'll report back when i dig into that in a few months.

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just a quick follow-up on this thread:

 

i completed my F54/P79 rebuild and swapped it in, transferring the carbs exactly as set up for the old motor and i've been delighted with how well it runs. the the new motor is broken in with about 700 miles on it and the carbs are performing flawlessly - beautiful, steady idle at 600rpm and silky smooth right up to 7K (haven't revved any further than that yet). i'm pretty sure there's more to get from them with some fine tuning, but that will wait until i install a 6-2-1 header and the dual O2 sensors to really understand where it's at. i'll report back when i dig into that in a few months.

Hey Rossiz, I thought I'd share some information I've gotten from Jeff G 78 on his 02 sensor placement on the header.  He just put one in, Innovate MTX-L 3844, and said there is very little room down there where the header runs against the tranny so the right angles of the bung are critical.  I know I had to grind off some of the transmission so my 6 to 1 header would fit on my '77, it was touching before the grinding.

 

I'll put up what he told me in a PM, hopefully he won't mind.  :o

 

"The bung comes with the kit.  Most bungs are 1/2" tall, but the one that comes with the kit is 1" tall, so if you buy a bung, you might want to get a tall one.  Get a plug if you don't plan to install the sensor right away.  The instructions say that the O2 sensor tip should be flush with the inside of the collector to protect it which is the reason for the tall bung.  The sensor body and lead wire with a 1" tall bung is very tall, so finding a spot where it fits is critical.  It has a range of angles where it can be installed from vertical.  I came very close to screwing up.  I thought I had the angle right when I marked it, but I underestimated the length of the sensor plus the wire.  I should have tipped it up a few more degrees.  As it is, the sensor wire touches the transmission and could rub.  I will add some convolute to protect it.  

 

The bung is also flat on both ends.  You will want to grind the pipe end to create a saddle so it fits the shape of the pipe to make welding easier.  It took 5 minutes with a die grinder to get the shape close.  A friend TIG welded it for me.

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hey site,

 

good info - thanks for the post. and thanks jeff G for passing on the experience. i have a dual-sensor unit and my plan is to swap out my current 6-1 for a 6-2-1 and put the sensors in the Y collector which will give me separate readings for the front and rear carbs. this will put them a bit higher into the engine bay and while it should eliminate tranny interference, i'm gonna have to watch out for the fender well - i'm hoping the angle of the Y will wind up putting them below/in front of the break booster. i'll be sure to post up when the time comes

 

these are the pics i'm using for reference:

 

MSA 6-1 (current)

post-28907-0-52830000-1440074928_thumb.j

 

MSA 6-2-1 & Y adaptor

post-28907-0-97067700-1440074928_thumb.j  post-28907-0-75202200-1440074928.jpg

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I currently run the 6-2-1 header but I only went with one O2 sensor at the end of my Y pipe.  I have been very happy with the results for many years. I have no idea how long the O2 sensor is good for, but she is chugging along with no issues. I have absolutely no idea if it is still accurate though :)

 

I love me some SU's they are wonderful carbs.

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finances and a new job have occupied me completely as of late, so i haven't had any time/extra cash to fiddle with the car (much less for a new exhaust system) so i've just been running on my "shade-tree" tune - my O2 sensors at present are comprised of ears, nose & eyes...

 

she's running rich, but not terribly so, and i'm sure when i get the O2 sensors installed i'll have fun dialing in the needles, but for now i'm quite impressed with just how reliable and hassle-free these carbs have been. i know the car isn't tuned to perfection yet, but it's running well, starts easily and the warmup/choke ritual is perfectly predictable. 

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I loved the SU's when I had them on my 77 rossiz. I had no trouble with them. IIRC they were on the Z for almost 7 years when I lived in Nevada. When we came back to California I had to put the EFI back on it. Wouldn't pass "visual" part of the emissions testing with the SU's. I do miss them. 

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Kind of my set up since I have 6-2 to duals. It's nice to be able to swap from front carbs to rear. Of course you have the odd man out with the center carb. When my idle was so funky, I found after switching the sensor back to front that I had a lean conditions. On #1 carb. When I richened it up mixture the idle got perfect. It's nice to be able to split your troubleshooting ability like that.

But then you spiral into the consuming obsession of perfect running carbs as you try to achieve 14.7

Sometimes I wish I just pulled the spark plugs and called it a day-LOL

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